The present invention is directed to a self-venting microwaveable package and its method of manufacture. The package is adapted to sealably contain a liquid or solid or semi-solid to be heated. When an air-tight unvented package is heated in a microwave oven, pressure builds up in the sealed package holding the product. After a critical internal pressure is reached, the package can explode, spattering its contents over the oven interior.
Numerous approaches have been utilized in attempts to solve this problem. One microwaveable package, illustrated in U.S. Pat. No. 5,298,708 to Babu, teaches a microwaveable tape that absorbs radiation and converts it to heat. The tape is actually secured onto the top of the bag to be microwaved. The tape is used to vent bags by absorbing radiation, convening it to heat, and then having the heat flow to the plastic, where it softens the plastic so that internal bag pressure bursts the plastic and allows the pressurized vapor to vent. This tape is not meant to form a peelable opening nor is it meant to vent by having the layers forming the seal of the bag separate. The tape is expensive to manufacture, especially the microwave active layer. Furthermore, the size and location of the hole formed in the bag is unpredictable, and may lead to spills either during microwaving or when trying to remove the substance heated. Thus, the package is unsuitable for holding liquids or semi-liquids.
Another microwaveable bag of the same type is taught by U.S. Pat. No. 4,640,838 to Isakson. In Isakson, a deposit of a microwave-absorbing substance such as graphite is deposited on the surface of the package. The package then operates just like that disclosed by Babu. This package has the same disadvantages as Babu does, i.e., it is unsuitable for use with liquids or semi-liquids.
Yet another prior art package is disclosed by U.S. Pat. No. 5,061,500, issued to Mendenhall. Mendenhall's package, primarily designed for popcorn, does not handle liquids well. The bag disclosed by Mendenhall was comprised of an outer layer of paper or polymer film, and an inner layer of a heat sealable polyester composite film. The bag lacked the structural strength to hold high-density fluids and viscous substances.
U.S. Pat. Nos. 4,576,285, 4,667,453 and 4,705,174, all to Goglio, lack the crucial self-venting feature of the instant invention. Furthermore, these inventions have excess multiple layers in the seal which are unnecessary, thus increasing the costs of manufacture and resulting in extra, wasteful pollution.
An easy open package is illustrated and described in U.S. Pat. No. 4,944,409. A tie layer forms a constituent layer of one package wall and is peelably bonded to one package wall and permanently bonded to another. The tie layer however is not in a limited strip area and adds a good deal of expense to the overall package and does not allow controlled venting.
None of the prior art patents provide a self-venting microwaveable package that is capable of holding liquids or semi-liquids, self-vents, provides for easy pouring of the heated product and is easily opened at its top closure without the need for additional structural material.